Smoking

Smoking is one of the major avoidable risk factors ofchronic, life-threatening diseases of the gas exchange and circulatory systems.

1. Describe the effects of tar and carcinogens in tobacco smoke on the gas exchange system with reference to lung cancer and chronic obstructive pulmonary disease (COPD)

Tar is a mixture of compounds that settles on the lining of the airways and in the lungs

Carcinogens are cancer-causing compounds that cause mutations in genes that control cell division

a) Chronic bronchitis

Tar stimulates the goblet cells and mucus glands to enlarge and secrete more mucous

Tar also inhibits the cleaning action of the ciliated epithelium

It destroys many cilia and weakens the sweeping action of those left

This causes mucus to accumulate in the bronchioles

As mucus is not moved, or moved very slowly, dirt, bacteria and viruses collect and block the bronchioles

With time, the damaged epithelia is replaced by scar tissue and the smooth muscle surrounding the bronchi and bronchioles becomes thicker

The thickening of the aiways causes them to narrow and makes breathing difficult

Pneumonia easily develops in the accumulated mucus and when there is an infection in the lungs, the linings become inflamed and this further narrows the airways

Sufferers have a severe cough and produce large quantities of phlegm

b) Emphysema

The inflammation of the constantly infected lungs cause phagocytes to line the airways

To reach the lining of the lungs from the capillaries, phagocytes release the enzyme elastase which destroys elastin in the walls of the alveoli to make a pathway for the phagocytes to destroy the bacteria

Elastin is responsible for the recoil of the alveoli

When there is a small quantity of elastin remaining in the alveolar walls, the alveoli do not stretch and recoil during inspiration and expiration

As a result, the bronchioles collapse during expiration, trapping air in the alveoli which often burst